<template>
  <div>
    <el-checkbox
      :indeterminate="isIndeterminate"
      v-model="checkAll"
      @change="handleCheckAllChange"
      >全选</el-checkbox
    >
    <div style="margin: 15px 0;"></div>
    <el-checkbox-group
      v-model="checkedCities"
      @change="handleCheckedCitiesChange"
    >
      <el-checkbox v-for="city in cities" :label="city" :key="city">{{
        city
      }}</el-checkbox>
    </el-checkbox-group>
  </div>
</template>
<script>
const cityOptions = ['上海', '北京', '广州', '深圳']
export default {
  data() {
    return {
      checkAll: false,
      checkedCities: ['上海', '北京'],
      cities: cityOptions,
      isIndeterminate: true
    }
  },
  methods: {
    handleCheckAllChange(val) {
      this.checkedCities = val ? cityOptions : []
      this.isIndeterminate = false
      //  console.log(this.checkedCities)
    },
    handleCheckedCitiesChange(value) {
      let checkedCount = value.length
      this.checkAll = checkedCount === this.cities.length
      this.isIndeterminate =
        checkedCount > 0 && checkedCount < this.cities.length
      //  console.log(this.checkedCities)
    }
  }
}
</script>
